Post treatment of desalinated and soft water for balanced water composition supply

Abstract

A calcite dissolution post-treatment process and apparatii for desalinated water are provided. The process comprises separating cations from seawater or brackish/seawater desalination brines by ion exchange resin(s) onto which the ions are loaded, contacting the ion exchange resin(s) loaded with the cations with an effluent of a calcite dissolution reactor wherein the cations are exchanged with Ca 2+ from this effluent. The Ca 2+ concentration of the resulting desalinated water decreases while the cations concentration increases to comply with required quality criteria. Batch type and continuous apparatii by which the process can be carried out are described.

1 . An H 2 SO 4 -based or CO 2 -based calcite dissolution post-treatment process for water or any other cation-rich solution comprising:
 separating cations from said water by at least one type of ion exchange resin onto which said ions are loaded; and   contacting said at least one ion exchange resin loaded with said cations with an effluent of a calcite reactor wherein said cations are exchanged with Ca 2+  from said calcite reactor effluent,   wherein the Ca 2+  concentration of the resulting desalinated water decreases while the cation concentration increases to comply with required quality criteria.   
     
     
         2 . The process as claimed in  claim 1 , wherein the water is seawater, brackish or seawater desalination-process brine. 
     
     
         3 . The process as claimed in  claim 1 , which further comprises rinsing said ion exchange resin with an internal desalination-plant water stream low in dissolved solids and draining it thereafter. 
     
     
         4 . The process as claimed in  claim 1 , wherein said cations are Mg 2+ , K +  and Na +  and wherein Mg 2+  ions are being exchanged in a first type ion exchange resin and Na +  and K +  ions in a second type ion exchange resin. 
     
     
         5 . The process as claimed in  claim 4 , wherein said first type ion exchange resin has a high affinity towards divalent cations such as Mg 2+  and Ca 2+  and an extremely low affinity towards monovalent cations such as Na +  and K + . 
     
     
         6 . The process as claimed in  claim 4 , wherein said second type ion exchange resin has a high affinity towards monovalent cations such as Na +  and K +  and a relatively low affinity towards divalent cations such as Ca 2+  and Mg 2+ . 
     
     
         7 . The process as claimed in  claim 5 , wherein said first type ion exchange resin is a resin such as Amberlite IRC747 (Rohm & Hass INC.) or equivalent. 
     
     
         8 . The process as claimed in  claim 1 , wherein said water used to load the resin with cations is filtered water before it enters desalination process. 
     
     
         9 . The process as claimed in  claim 8 , wherein the water used to load the resin with said cations is pre-filtered using sand filtration or UF membranes. 
     
     
         10 . The process as claimed in  claims 9 , wherein said water that is used to load the resin is returned back to a container from where it was taken in a closed loop manner or discarded. 
     
     
         11 . The process as claimed in  claim 1 , wherein the process is carried out in a batch ion-exchange mode. 
     
     
         12 . The process as claimed in  claim 1 , wherein the process is carried out in a continuous ion exchange mode. 
     
     
         13 . The process as claimed in  claim 1 , wherein the required quality criteria is Alkalinity (H 2 CO 3 * alkalinity) greater than 80 mg/L as CaCO 3 ; Ca 2+  higher than 80; Calcium Carbonate Precipitation Potential between 3 and 10 mg/L as CaCO 3  and pH of less than 8.5. 
     
     
         14 . The process as claimed in  claim 1 , wherein the process can be implemented in order to replace any certain fraction of the Ca 2+  concentration generated by H 2 SO 4 - or CO 2 -based calcite dissolution processes or a combination of both by an equivalent cations concentrations.